The present invention relates generally to cogeneration systems, and specifically to an improved cogeneration system having an exhaust heat exchanger with an integral catalytic converter element.
Cogeneration is an energy-production process involving the simultaneous generation of thermal (e.g. process steam) and electrical energy by using a single primary heat source. It can be employed whenever there is a need for the two energy forms and whenever on-site electric power generation is justified or when thermal-energy users are in close proximity to an electric power generation site. For example, packaged natural gas fueled cogeneration systems are available from Tecogen, Inc. of Waltham, Massachusetts, assignee of the present invention, in several different output ratings (e.g., 60 KW of electrical power, 440,000 BTU/hr thermal output as hot water). Such cogeneration systems are often used by hospitals, health clubs having large heated swimming pools, greenhouses, schools and light industry.
Fuel saving is a major incentive for use of cogeneration. Since all heat-engine-based electric power systems exhaust heat to the environment, the exhausted heat can frequently be used to meet all or part of the on-site or local thermal energy needs. Use of the exhausted heat does not normally affect the amount of primary fuel used, yet it can lead to a saving in all or part of the fuel that would otherwise be used for the thermal-energy process.
The cogeneration system toward which the present invention is directed utilizes a fossil fuel burning internal combustion engine in which exhaust gas is directed through a heat exchanger to heat water for use as "hot water". This exhaust gas is generally at 1000.degree.-2500.degree. F. entering the heat exchanger, and in passing through the heat exchanger heats water circulating through a coil whose external surfaces are contacted by the exhaust gas. Before the exhaust gas can be discharged into the atmosphere, it may require a treatment in a catalytic converter which heretofore has been provided as a separate unit upstream of the heat exchanger. The converter may typically contains a noble metal catalyst, a material which promotes the reduction of NO.sub.x and conversion of the carbon monoxide and hydrocarbons which result from partly burned or unburned fuel to carbon dioxide and water vapor. The exhaust gas is thus sufficiently clean for discharge into the atmosphere.
A principal disadvantage of known cogeneration systems with catalytic converters is that the systems are large and bulky, requiring considerable space and external plumbing of their separate, interconnected components. The cost of such cogeneration systems accordingly may be higher than desired. A decrease in size of the system would reduce costs and result in a cogeneration system which could fit the space requirements of a larger number of potential users.
Accordingly it is a principal object of the present invention to provide a cogeneration system having a catalytic converter and which is compact and space efficient.
It is a particular object of the invention to provide a single or multi-stage catalytic converter arranged within the housing of an exhaust gas heat exchanger of a packaged cogeneration system.
Another object of the present invention is to provide a cogeneration system that can be economically produced and thus available to a wide range of users.
These and other objects and advantages of the present invention will be evident from the description which follows.